1. Field of the Invention
This invention relates to a method for producing an InSb thin film element which has very little current noise and which can make the signal-to-noise ratio great.
2. Description of the Prior Art
InSb (indium antimonide) which is one of compound semiconductors exhibits a remarkable galvano-magnetic effect. Therefore, it is often used for magneto-electric transducers such as Hall generator and magneto-resistive element. Since, at this time, InSb is required to be very thin, the physical evaporation process such as vacuum deposition or the chemical evaporation process such as well-known CVD (chemical vapor deposition) (hereunder, these processes shall be briefly termed "evaporation processes") is employed for the production of an InSb film. As the thickness of the InSb film, a value of roughly 3-0.1 .mu.m is employed. A thickness below 0.1 .mu.m is unsuitable for practical use because the level of noise itself is too high. The InSb thin film produced by the evaporation process is a polycrystalline film in which the crystal grain size is 1-20 .mu.m in diameter and which includes many crystal defects. In order to coarsen crystal grains and to diminish the crystal defects, there has been adopted the zone-melting treatment of the InSb film. Even with this treatment, however, the grain size becomes 0.5-2 mm at the utmost, and the crystal defects cannot be completely removed. In case where an element is formed of such an InSb film and current is caused to flow therethrough, noise is superposed on the output thereof. The extent of the noise is as stated below by way of example. The example is of a case where a current of 4,000 A/cm.sup.2 was caused to flow through a Hall generator having a film thickness of 2 .mu.m and a generator width of 200 .mu.m. When an evaporated InSb film was used, noise of 2-10 .mu.V developed between Hall voltage terminals. When an InSb film subjected to the zone melting was used, noise of 0.6-2 .mu.V appeared. These values are the root-mean-square values of noise voltages observed in a frequency band of 100 Hz-10 KHz. The Hall coefficients R.sub.H of such films were approximately 300-350 cm.sup.3 /C. When the signal magnetic field was 10 G, the above element provided an output of 2.5-2.8 mV. With the prior-art InSb film subjected to the zone melting, accordingly, the signal-to-noise ratio was 63-73 dB in the case of the above element. It was difficult to attain a higher signal-to-noise ratio.
In general, the behaviors of impurities in an InSb bulk single crystal have been investigated well. Regarding the InSb polycrystalline thin film, there have been reported an example in which the film is doped with Ge to the end of improving the temperature characteristic of the Hall coefficient, an example in which it is doped with S to the end of facilitating the zone melting, etc. In this connection, reference may be had to Japanese Unexamined Published Patent Application No. 49-135588 and U.S. Pat. No. 3,591,429 (1971) to A. R. Clawson et al. The behaviors of impurities in a polycrystal, however, have not been revealed. The inventors studied the effect of the impurity doping with notice taken of the signal-to-noise ratio of the InSb thin film element, and have led to this invention.